This disclosure relates generally to the field of providing digital feedback in isolated systems.
In isolated systems, like flyback converters, the input circuitry (i.e., the “Primary Controller”) and the output circuitry (i.e., the “Secondary Controller”) are not electrically/galvanically connected to each other. Flyback converters are commonly used as isolated battery chargers and/or front-end AC-DC and DC-DC converters in switch mode power supply applications. For example, a common flyback converter is a buck-boost converter including an inductor that is split to form a transformer. A primary winding of the transformer is coupled to the input circuitry, and a secondary winding of the transformer is coupled to the output circuitry, thus providing the desired isolation between the input circuitry and the output circuitry. Therefore, any communication between the two modules must be carried out by some form of opto-isolator or optocoupler device.
Since optocouplers are relatively bulky and costly, it is prudent to limit the quantity of optocouplers that will be used in a given circuit. However, certain information must be passed from the secondary or output side of the converter to the Primary Controller for proper system regulation. For example, information regarding output voltage and/or current regulation, short circuit, output over voltage, output under-voltage, and over temperature are some of the exemplary signals that may be passed from the output side of the converter to the Primary Controller in a given implementation.
In standard configurations, the key signals are passed from the Secondary Controller to the Primary Controller through the pin that controls the loop regulation, also referred to herein as the “COMP node.” For example, in certain fault conditions, such as output system shorts to ground, the flyback converter can't react immediately to rectify the problem. When the output system voltage drops to abnormal levels, the COMP node rises to correct the problem. When the COMP node rises high enough, i.e., beyond the dynamic range of the controller, the over current protection circuit triggers to limit the current or turn off the system. Unfortunately, the response time for this behavior is limited by the bandwidth of the system, which can be quite slow, e.g., in the range of 5 kHz to 10 kHz. This latency can be problematic and harmful to the output system—even leading to its potential destruction.
In the embodiments described herein, systems and methods are proposed by which a plurality of different fault conditions may be digitally transmitted from the secondary side to the primary side of the converter fast enough so that the Primary Controller may be turned off before any subsequent complications can occur in the output system.